Testing means to sustain short-term early childhood development impacts long-term Abstract An estimated 43% of the world?s children under age 5 in low-income and middle-income countries (LMICs) do not reach their full developmental potential due to poverty, nutritional deficiencies, and inadequate psychosocial stimulation. Early childhood development (ECD) interventions that promote parent-child interaction through psychosocial stimulation and nutrition activities can improve short-term child development outcomes in LMIC settings. However, despite some flagship successes, many studies have shown that early program benefits fade over time. These findings suggest that achieving parental adherence to new behaviors long-term is the next significant challenge for ECD interventions. Our parent R01 NICHD study is conducting a multi-arm clustered randomized controlled trial across 60 villages and 1200 households with children aged 6-24 months in rural Kenya. The trial tests different potentially cost-effective delivery models for an ECD intervention with a parent-focused curriculum that integrates child psychosocial stimulation and nutrition education in biweekly village-based sessions lasting seven months. In summer 2019, our parent study will conduct an endline survey to measure impacts on child developmental outcomes and parental behavioral changes immediately following the intervention period, as well as a follow-up survey two years later to measure sustained behavioral changes and impacts on children. Between the endline and follow-up surveys, one study arm is currently scheduled to receive two ?booster? sessions within 6 months following the end of the biweekly village sessions to encourage families to sustain the behavioral changes. This leaves a 1.5 year gap with no planned activities under the parent study. In this R21 project, we propose an expansion to our parent study to extend these ?booster? visits by an additional year and a half to fill this gap in one study arm, and randomly varying the number of boosters across households in this arm to test for a dose-response relationship between continued program support and sustained outcomes. This extension would enable selected households to receive bimonthly boosters for up to the full two-year period between the parent study?s endline and follow-up surveys. These boosters will be designed to address key barriers to sustained behavioral changes and feature curriculum that scaffolds on the earlier intervention in order to help parents adopt new strategies and activities that grow in complexity to match their children?s maturing capabilities. Overall, this extension offers 3 key benefits over the parent study: 1) it strengthens our ability to learn about the importance of continued program engagement and practice to engender sustained parental behavioral changes, as well as sustained child developmental impacts to overcome the problems of fade-out that have plagued earlier ECD trials; 2) it allows us to test the impact of differential exposure to such continued support, which is key to inform policy; and 3) it allows us to examine the role of an age-appropriate curriculum that adapts to children?s evolving needs over time in achieving sustained impacts.